Communications devices including wireless terminals for personal communication systems and the like conventionally use a receiver which is held close to the user's ear during operation for both privacy and good audio quality. Recently, however, devices have been developed which also include a loudspeaker, either as an integral part of the terminal, or as an accessory, to provide either just handsfree listening (receive mode) or as part of a complete handsfree (transmit and receive) system.
Users of such telephone services as voice mail and automated answering systems often find it more convenient to navigate these services through the use of the dial pad while listening to instructions through the loudspeaker as opposed to continuously moving the receiver away from the ear to see the dial pad. This becomes even more important when the terminal has an integral display which the user needs to see and perhaps write on while listening.
Conventional terminals also use a separate transducer, typically a piezo or a magnetic sounder, for providing alerting functionality (ringing or buzzing). The capabilities of these transducers are generally quite limited, thereby limiting the loudness and/or the audio quality of the alerting signal.
In the interest of conserving space and minimizing component and assembly costs it would be advantageous to provide both handset and handsfree receive modes of operation (or simply handset and handsfree modes) with a single transducer. At the same time, of course, the audio quality must satisfy various industry standards and meet user expectations while the terminal is either loosely or tightly coupled to the ear in handset mode, or at some distance from the user's ear in handsfree mode. One such standard requires that the frequency response delivered by the loudspeaker to the user in both handset and handsfree modes be relatively flat over a frequency range of 300 to 3300 Hz. It is also expected that the overall output signal level in handset mode be lower than in handsfree mode. When a loudspeaker that provides a flat frequency response in handsfree mode is used in handset mode, where the output signal level is lower, the frequency response in handset mode will emphasize lower frequencies over higher frequencies. Therefore, to maintain acceptable audio, the relative amplitude of the lower frequencies produced by the loudspeaker in handset mode must be reduced.
Further reduction in the space required and cost of manufacture can be attained by providing the alerting functionality with the same transducer used in handset and handsfree modes. Given a way to evaluate the proximity of the user to the terminal, the alerting signal could be made loud when the user is far from the terminal, yet soft when the user is close to the terminal.
As indicated previously, some manufacturers of wireless terminals have both handset and handsfree functionality in their products. These products, however, achieve dual mode operation through the use of separate transducers for each function.
It is also known to use "leak-insensitive" or "low acoustic output impedance" receivers in order to provide good audio quality when the terminal is loosely coupled to the ear. However, such receivers do not provide handsfree functionality.